II. DESCARTES AND HIS SUCCESSORS
Though it is customary to contrast Hume's empiri-
cism with the rationalism of Descartes and the Conti-
nental philosophers whom he influenced,
their discus-
sions of causal explanation
had certain important
features in common. One was concern about the
notion
of force. Descartes and the occasionalists, attacking
what they
took to be animistic conceptions of forces
in nature, raised questions
about the origin of the idea
of force; and Nicolas Malebranche, employing
argu-
ments like Hume's, reached
essentially the same con-
clusions as Hume
did—much later in a nontheological
manner—about
causal statements in science and in
daily life. A second common feature was
the view that
physics was concerned with efficient causes and not
with
final causes. While Descartes was prepared to
admit that there were causes
other than efficient
causes—for instance, that created things
could be
viewed as serving God's purposes, and also that God
as
causa sui was not, strictly speaking, the
efficient
cause but rather the formal cause of His
existence—he
insisted that in physics only efficient causes were
to
be investigated. Spinoza, also imposing this restriction,
rejected
outright the doctrine of final causation and
also rejected Descartes'
distinction of God's formal
causation of Himself and efficient causation of
the
universe.
In Principia philosophiae (1644), Descartes,
laying
down the rule that efficient and not final causes were
to be
investigated (Part I, Princ. xxviii), was concerned
to banish several kinds
of explanations in physics.
Although he thought that ends or purposes could
be
attributed to creatures having a soul or mind and also
to God,
“God's purposes... seem to be hidden in the
abyss of His
inscrutable wisdom”; and, while some
parts of nature served our
purposes, to say that they
were created for this reason would have been
con-
jecture and not an expression of
genuine knowledge.
Proposing this rule, Descartes also had in mind
certain
kinds of statements and explanations that he found in
scholastic manuals, for example, that heavy bodies
sought the center of the
earth. To say that heavy bodies
sought the center of the earth was to
impute to these
bodies characteristics that, according to Descartes,
could only be ascribed to beings having a soul or mind.
In letters to the Princess Elizabeth (May 21 and June
28, 1643, in Correspondance, ed. Adam and Milhaud,
V, 289-92,
322-25), he distinguished four primitive
notions under which all of our
ideas could be subsumed
and pointed out what he took to be misapplications
of certain ideas, or category mistakes, in scholastic
physics.
In addition to (1) ideas that were applicable
to any conceivable
entity—e.g., being, number, and
duration—there were
(2) ideas that could be applied
only to bodies, namely, ideas of their
extension, shape,
and motion; (3) ideas under the category of thought
that pertained only to souls or minds; and (4) ideas
applicable to the
union of soul and body in a human
being, including an idea of the
“force that the soul
has of moving the body.” When,
according to Des-
cartes, the scholastics
explained the behavior of heavy
bodies by asserting that their weight made
them seek
the center of the earth, they misapplied ideas of the
third
and fourth categories. They conceived of weight
as an unextended entity
that was supposed to be in
some way attached to an extended body yet could
also
be removed if the body ceased to be heavy. This
quasi-substantial
unextended entity, or “real property,”
was, as it
were, a small soul; and the animism of the
scholastics consisted in part in
their imputing to in-
animate objects entities
with characteristics of the third
category that could only be applied to
beings having
a soul or mind. They also thought of the weight of
a
body as exerting force and acting on the body; and,
so doing, they
misapplied an idea of the fourth cate-
gory—namely, of the force that the soul has of moving
the
body—to entities that were to be described exclu-
sively in terms of their geometrical properties and
motion and rest.
Although Descartes took exception to what he
thought was an animistic or
anthropomorphic concep-
tion of force in
scholastic physics, he made use of terms
like “force”
in his own physics. Stating his principle
of inertia, for instance, he
maintained that “once a
body has begun to move, it has in itself
a force to
continue its motion...” (letter to Mersenne,
October
28, 1640). In attributing an inertial force to moving
bodies,
he did not think that he was imputing to them
the kind of force experienced
in voluntary action; for,
as he carefully explained, the force that he
attributed
to a moving body—its “quantity of
motion”—could
be defined in terms of the clearly and
distinctly per-
ceived properties of motion
and (ultimately) volume.
Commentators have raised questions about Des-
cartes' attempt to explain what he meant by terms like
“force” and “tendency to move” by
reference to mo-
tion and rest and the
geometrical properties of bodies.
In his physics, he distinguished the
motion that a body
tended to have from its actual motion; and, making
this distinction, it seems that he could not consistently
identify force,
or quantity of motion, with the product
of mass or volume and actual
motion. In the last year
of Descartes' life, Henry More raised an objection
of
this kind: he was unable to reconcile Descartes' con
tention that motion, like shape, was a mode or state
of a body
and his assertion that motion could be trans-
ferred or communicated from one body to another. In
his reply,
Descartes found it necessary to make a dis-
tinction. Motion, in the sense of translation from place
to
place, was, like shape, a mode or state of a body.
But this was to be
distinguished from a body's moving
force (vis
movens), which he explained “can be God's,
conserving
the same amount of motion in matter as
he placed in it from the first
moment of creation; or
also that of a created substance, such as our mind;
or
that of any other thing to which God gave the force
of moving a
body” (August, 1649, Correspondance,
VIII, 264). This explanation left the question open as
to whether God had
bestowed this force on bodies
themselves. But Descartes added that he had
not dis-
cussed the matter in his published
writings for fear of
giving the impression that, on his view, God was
the
soul of the world; and he implied, though he did not
clearly
assert, that the moving force of bodies was not
to be attributed to bodies
but to God. It seems that,
when More pointed out an ambiguity and
Descartes
found it necessary to make a distinction, it was difficult
for him to say unequivocally where the force that he
had distinguished from
motion was located. If he at-
tributed it to
bodies, he would have been imputing
to them a property admittedly other
than motion and
extension, and his own view would have been subject
to
the kind of objection that he had raised regarding
the forms and qualities
of the scholastics. Yet he needed
the notion of a body's force, or quantity
of motion,
to explain its behavior. His last words on the subject
expressed an inclination to consign this putative prop-
erty of bodies of God.
In his published writings, Descartes had claimed that
God was the primary
and universal cause of motion
(Principia, Part II,
Princ. xxxvi), and he had explained
that, but for God's imparting motion to
matter in the
beginning and continuing to impart motion by his
“ordinary concourse,” matter would have been a
homogeneous substance undifferentiated by the motion
of its parts. He was
clearly on record that the divine
concourse, or God as causa secundum esse, was a
necessary condition of the motion
of bodies. Accepting
this view, the occasionalists employed a variety
of
arguments to show that God was also the sufficient
condition of a
body's moving, and that a body of itself
lacked the power to continue its
motion or to commu-
nicate it to other
bodies. In Méditations chrétiennes
et
métaphysiques (1683), Malebranche argued that, in
conserving a body from moment to moment, God must
continue to will either
that it exist in the same place
or that it exist in different places. If He
willed that
it exist in the same place, the body was necessarily
at rest. God's will was inviolable, and nothing could
make a
body move that He had willed to be at rest.
In similar fashion, if God
willed that a body exist
successively in different places, nothing could
keep it
from moving to those places. Since the motion or rest
of
bodies was determined necessarily by the will of
God, Malebranche concluded
that bodies could not
move themselves or other bodies and that the
moving
force of bodies was the will of God.
To Malebranche, the inefficacy of bodies—and in-
deed of any “second
cause”—seemed to be a direct
consequence of
Descartes' doctrine of divine con-
servation. But he also supported his conclusion in other
ways. In
Éclaircissement XV, appended to his De la
recherche de la vérité...
(1674-75), he maintained that
we could not form a clear idea of the
putative force
in bodies nor indeed of the force allegedly exercised
in human volitions. He held that, when we consulted
our clear and distinct
idea of the essence of a body,
we discovered that it was necessarily
extended, divisi-
ble, and movable; but, in
consulting this idea, we could
not discover the force that it was supposed
to have
to move itself or other bodies. If such a force could
be
discovered from an investigation of an idea of a
body, it would have been
possible to determine a priori
and without recourse
to experience how it would move.
It would have been possible, for example,
to determine
a priori and without recourse to experience that,
when
a billiard ball in motion came in contact with another
ball that
was at rest, the second ball would move off
in a certain direction. There
was, however, no neces-
sary connection
between the motion of the first ball
and that of the second, and the
behavior of the second
ball could not be determined a
priori. It was only from
experience that we learned that the
second ball would
move in a certain way. Since our experience of regu-
larities in the behavior of moving
bodies was abundant,
the mind moved with great facility from the
thought
of the first ball coming in contact with the second to
the
thought of the second ball moving; and, as a result,
we tended to think
that there was a necessary connec-
tion and
that one event was the true cause of the other.
This, however, was a
mistake. The two events were
distinct and not necessarily connected; and,
for Male-
branche, the only necessary
connection to be discov-
ered between
distinct events was between the volition
of an omnipotent being and its
execution.
In similar fashion, Malebranche argued against the
efficacy of human
volitions. To show that we lacked
a clear idea of the mind's alleged power
to move the
body, he maintained that there was only a contingent
connection between a volition and movement of the
part of the body that was
willed. Moreover, the effort
that we sometimes experienced in attempting to move
a part of our bodies did not provide us with an idea
of
efficacy or necessary connection, for effort of this
sort was not always
successful. Like Hume, he also
appealed to our ignorance of the cerebral
mechanics
required to move parts of the body and to our failure
to
understand how a volition could bring about motion
of physical particles in
the brain.
Although Melebranche proclaimed that God does
everything (Dieu fait tout), he did not deny outright
or
unqualifiedly that bodies or minds were causes.
Following the precedent of
Géraud de Cordemoy in
Le Discernement du corps et de l'âme
(1666), he distin-
guished the real or
true cause, on the one hand, and
the occasional or particular or natural
cause, on the
other. When one billiard ball came in contact with
a
second and the second moved, the impact of the first
ball could be called
the occasional cause of the second
ball's moving. To say that it was the
cause in this sense
was simply to say that the second ball moved on
the
occasion of contact with the first ball and that events
of the one
kind regularly followed events of the other
kind. About the analysis of
causal statements of this
sort, Malebranche and Hume were of the same
mind.
Hume was aware of this similarity, but he chose to
stress the
difference between his view and that of the
occasionalists. The
occasionalists distinguished two
kinds of causes; whereas, according to
Hume, “all
causes are of the same kind...,” and there
was “no
foundation for that distinction... betwixt cause and
occasion.” It is fair to say that, in
rejecting this distinc-
tion and claiming
that all causes were of the same kind,
Hume expressed what was truly
original in his view
about causation.
Benedict Spinoza, rejecting the Cartesian distinction
of God and nature,
also took exception to certain
Cartesian views about causation. While
Descartes ban-
ished final causes from physics
on the ground that they
were unknowable, Spinoza, in the famous
Appendix
to Part I of his Ethica (published
posthumously, 1678),
maintained that the notion of final causation in
nature
or in God was rationally indefensible. To suppose, he
argued,
that God acted for certain ends entailed that
He sought something of which
He was in need, and
this consequence was incompatible with the divine
perfection. Earlier, in Part I of the Ethica, he had
also
argued that the supposition of God acting for an end
could not be
reconciled with divine omnipotence or,
properly interpreted, divine
freedom. Rejecting the
view that things in nature were created to serve
our
ends, he maintained that everything followed of neces-
sity from the divine nature; and, contrary to
Descartes,
he claimed that God was cause of Himself in the same
sense
in which He was cause of all other things, namely,
as efficient cause. It
has been noted, however, that
Spinoza's conception of an efficient cause was unlike
Descartes' and also Hume's. While agreeing with
Descartes that an efficient
cause need not be tempo-
rally prior to its
effect, he conceived of God as
causa
immanens, that is, as not producing anything outside
of, or
distinct from, Himself; and, though he antici-
pated Hume's view that all causes were of the same
kind,
Spinoza's God and also the fixed and eternal
things causing individual
mutable things were not
temporally prior to, nor in reality distinct from,
their
effects.
